package jacky.lanlan.song.util.codec;

/**
 * Encodes data to Base64 and decodes it.
 * 
 * @author Stefan Laubenberger
 * @version 20080810
 */
public abstract class Base64Codec {
	// Resources
	private static final String RES_ILLEGAL_CHARACTER = "ConverterBase64.illegal"; //$NON-NLS-1$

	private static final String RES_INVALID_STRING = "ConverterBase64.invalid"; //$NON-NLS-1$

	private static final char[] map1 = new char[64];

	private static final byte[] map2 = new byte[128];

	// Mapping table from 6-bit nibbles to Base64 characters.
	static {
		int ii = 0;
		for (char c = 'A'; c <= 'Z'; c++) {
			map1[ii++] = c;
		}
		for (char c = 'a'; c <= 'z'; c++) {
			map1[ii++] = c;
		}
		for (char c = '0'; c <= '9'; c++) {
			map1[ii++] = c;
		}
		map1[ii++] = '+';
		map1[ii] = '/';
	}

	// Mapping table from Base64 characters to 6-bit nibbles.
	static {
		for (int ii = 0; ii < map2.length; ii++) {
			map2[ii] = (byte) -1;
		}
		for (int ii = 0; ii < 64; ii++) {
			map2[map1[ii]] = (byte) ii;
		}
	}

	/**
	 * Encodes a string into Base64 format. No blanks or line breaks are inserted.
	 * 
	 * @param string
	 *          String to be encoded.
	 * @return String with the Base64 encoded data.
	 */
	public static String encode(final String string) {

		final String str = new String(encode(string.getBytes()));

		return str;
	}

	/**
	 * Encodes a byte array into Base64 format. No blanks or line breaks are
	 * inserted.
	 * 
	 * @param in
	 *          Array containing the data bytes to be encoded.
	 * @return Character array with the Base64 encoded data.
	 */
	public static char[] encode(final byte[] in) {

		final char[] result = encode(in, in.length);

		return result;
	}

	/**
	 * Decodes a byte array from Base64 format.
	 * 
	 * @param string
	 *          Base64 String to be decoded.
	 * @return Array containing the decoded data bytes.
	 * @throws IllegalArgumentException
	 */
	public static byte[] decode(final String string) {

		final byte[] result = decode(string.toCharArray());

		return result;
	}

	/**
	 * Decodes a byte array from Base64 format. No blanks or line breaks are
	 * allowed within the Base64 encoded data.
	 * 
	 * @param in
	 *          Character array containing the Base64 encoded data.
	 * @return Array containing the decoded data bytes.
	 * @throws IllegalArgumentException
	 */
	public static byte[] decode(final char[] in) {

		int iLen = in.length;

		if (iLen % 4 != 0) { throw new IllegalArgumentException(RES_INVALID_STRING); }

		while (iLen > 0 && in[iLen - 1] == '=') {
			iLen--;
		}

		final int oLen = (iLen * 3) / 4;
		final byte[] out = new byte[oLen];

		int ip = 0;
		int op = 0;
		while (ip < iLen) {
			final int i0 = in[ip++];
			final int i1 = in[ip++];
			final int i2 = (ip < iLen ? in[ip++] : 'A');
			final int i3 = (ip < iLen ? in[ip++] : 'A');

			if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127) { throw new IllegalArgumentException(RES_ILLEGAL_CHARACTER); }
			final int b0 = map2[i0];
			final int b1 = map2[i1];
			final int b2 = map2[i2];
			final int b3 = map2[i3];

			if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0) { throw new IllegalArgumentException(RES_ILLEGAL_CHARACTER); }

			final int o0 = b0 << 2 | b1 >>> 4;
			final int o1 = (b1 & 0xf) << 4 | b2 >>> 2;
			final int o2 = (b2 & 3) << 6 | b3;
			out[op++] = (byte) o0;
			if (op < oLen) {
				out[op++] = (byte) o1;
			}
			if (op < oLen) {
				out[op++] = (byte) o2;
			}
		}

		return out;
	}

	/*
	 * Private methods
	 */
	/**
	 * Encodes a byte array into Base64 format. No blanks or line breaks are
	 * inserted.
	 * 
	 * @param in
	 *          Array containing the data bytes to be encoded.
	 * @param iLen
	 *          Number of bytes to process in <code>in</code>.
	 * @return Character array with the Base64 encoded data.
	 */
	private static char[] encode(final byte[] in, final int iLen) {

		final int oDataLen = (iLen * 4 + 2) / 3; // output length without padding
		final int oLen = ((iLen + 2) / 3) * 4; // output length including padding
		final char[] out = new char[oLen];
		int ip = 0;
		int op = 0;

		while (ip < iLen) {
			final int i0 = in[ip++] & 0xff;
			final int i1 = ip < iLen ? in[ip++] & 0xff : 0;
			final int i2 = ip < iLen ? in[ip++] & 0xff : 0;
			final int o0 = i0 >>> 2;
			final int o1 = (i0 & 3) << 4 | i1 >>> 4;
			final int o2 = (i1 & 0xf) << 2 | i2 >>> 6;
			final int o3 = i2 & 0x3F;
			out[op++] = map1[o0];
			out[op++] = map1[o1];
			out[op] = op < oDataLen ? map1[o2] : '=';
			op++;
			out[op] = op < oDataLen ? map1[o3] : '=';
			op++;
		}

		return out;
	}
	
}
